PIP: The identification of a small number of cases of clinical immunodeficiency and CD4 depletion but no evidence of human immunodeficiency virus (HIV) has raised questions as to whether a new virus that causes a syndrome similar to HIV infection has emerged. Most intensively studied have been 5 individuals from the New York area--2 homosexual men, 2 heterosexual men, and 1 female blood transfusion recipient--in whom no other cause of the immunodeficiency could be identified. Scientists at HIV treatment centers in Europe and other parts of the US have encountered similar cases, and the causative agent has been termed human intracisternal virus. It must be confirmed that the patients affected have antibodies to the putative agent before a definite link to acquired immunodeficiency syndrome can be established. In addition, it is premature to determine whether a new rare virus has indeed emerged or whether another form of HIV has evolved.